We have analyzed the propagation of light into tissue. Our calculations indicated that scatter is a critically important property of light-tissue interactions. The effects of scatter have not be extensively calculated nor appreciated. We proposed to use scatter to cause limited subsurface thermal damage to the dermis for non-ablative skin toning and rhytids reduction. We term this innovative laser delivery idea scatter-limited phototherapy. This proposed research project will test the scatter-limited phototherapy concept and apply it to the treatment of solar elastosis. To accomplish our goal, we will construct a scatter-limited phototherapy device to treat solar elastosis. This device will be designed to be used with a Nd:YAG laser (1064 nm). Using in-vitro samples of human skin, the temperature profiles, both spatially and temporally, will be measured using thermocouple probes. The contraction of the tissue after the treatment will also be measured using a photographic technique. We plan to establish that the scatter-limited phototherapy device is able to cause sub-surface collagen damage without causing the removal of the epithelial layer of cells. We will also test the scatter-limited phototherapy system on a piglet model. The piglet provides a skin model that is similar to human skin. Finally, we will investigate the wound healing in the piglet model using extracellular matrix studies. This research proposal should permit us to establish that scatter-limited phototherapy is efficacious and move from the laboratory investigations to prepare for human clinical trials. We expect that we will be able to pair this technology with a company and to apply for funding with an STTR grant. We also expect that this technology can be applied to other therapies besides the treatment of skin for solar elastosis. The technique of scatter- limited phototherapy could also be used in hair removal, or the treatment of soft palate to reduce snoring.